The present invention relates to a method of operating an internal combustion engine in a motor vehicle in particular, where fuel is injected directly into a combustion chamber either during a compression phase in a first operating mode or during an intake phase in a second operating mode, where shifting takes place between the two operating modes, and where the performance quantities that influence the actual moment of the internal combustion engine are controlled and/or regulated differently as a function of a setpoint moment in both operating modes. In addition, the present invention concerns an internal combustion engine for a motor vehicle in particular, having an injection valve with which fuel can be injected directly into a combustion chamber either during a compression phase in a first operating mode or during an intake phase in a second operating mode, and having a control unit for shifting between the two operating modes and for differential control and/or regulation of performance quantities that influence the actual moment of the internal combustion engine in both operating modes as a function of a setpoint moment.
Systems for direct injection of fuel into the combustion chamber of an internal combustion engine are conventional in general. A distinction is made between stratified operation as a first operating mode and homogeneous operation as the second mode. Stratified operation is used at relatively low loads on the internal combustion engine in particular, while homogeneous operation is used at relatively high loads.
In stratified operation, fuel is injected into the combustion chamber during the compression phase of the internal combustion engine, so there is a cloud of fuel in the immediate vicinity of a sparkplug at the time of ignition. This injection may occur in various ways. For example, it is possible for the injected cloud of fuel to be at the sparkplug and be ignited by it during or immediately after injection. It is also possible for the injected cloud of fuel to be carried to the sparkplug by the motion of a charge and only then ignited. There is not a uniform distribution of fuel with either combustion method, but instead there is a stratified charge.
The advantage of stratified operation is that the internal combustion engine can handle lower loads with a very small amount of fuel. However, higher loads cannot be handled by stratified operation.
In homogeneous operation which is intended for such higher loads, fuel is injected during the intake phase of the internal combustion engine, so that turbulence can be created in the fuel, which is thus readily distributed in the combustion chamber. Homogeneous operation thus corresponds approximately to the operation of internal combustion engines where fuel is injected into the intake manifold in the traditional manner. If necessary, homogeneous operation may also be used at lower loads.
In stratified operation, the throttle valve in the intake manifold leading to the combustion chamber is opened wide, and combustion is controlled and/or regulated only by the fuel mass to be injected. In homogeneous operation, the throttle valve is opened and closed as a function of the required moment, and the fuel mass to be injected is controlled and/or regulated as a function of the air flow intake.
In both operating modes, i.e., in stratified operation and in homogeneous operation, the fuel mass to be injected is additionally controlled and/or regulated at an optimum level from the standpoint of saving fuel, reducing exhaust, etc., as a function of a plurality of additional performance quantities. The control and/or regulation here is different in both operating modes.
The internal combustion engine must be shifted from stratified operation to homogeneous operation and back again. In stratified operation, the throttle valve is opened wide, and air is thus supplied largely without throttling, but in homogeneous operation the throttle valve is only partially opened, thus reducing the supply of air. Especially when shifting from stratified operation to homogeneous operation, the ability of the intake manifold leading to the combustion chamber to store air must be taken into account. If this is not taken into account, shifting (from one type of operation to another) can lead to an increase in the moment delivered by the internal combustion engine.
The object of this present invention is to provide a method for operating an internal combustion engine so that improved shifting between the operating modes is possible.
This object is achieved with a method of the type defined in and with an internal combustion engine according to the present invention by determining a change in the actual moment during a shifting operation and influencing at least one of the performance quantities as a function thereof.
On the basis of the determination of changes in the actual moment during the shifting operation, it is possible to detect irregular running or bucking while shifting. After bucking has been detected, the irregular running can be counteracted by influencing performance quantities. It is thus possible to prevent irregular running or bucking when shifting from homogeneous operation to stratified operation or vice versa. Shifting operations between the two operating modes are thus improved in particular with regard to smoother running and thus greater comfort.
In an advantageous embodiment of the present invention, the change in the actual moment is determined when shifting from the first operating mode to the second. This is a simple but effective method of detecting changes in the actual moment in a quasi-steady-state manner.
In another advantageous embodiment of the present invention, the change in the actual moment is determined in particular in succession at different fillings of the combustion chamber. In this way, dynamic shifting jerk is detected in a quasi-steady-state manner in dynamic operation of the internal combustion engine. This shifting jerk can be counteracted in the sense of minimizing it by dynamically influencing the performance quantities of the internal combustion engine.
In an advantageous embodiment of the present invention, the change in the actual moment is determined as a function of the measured rpm of the internal combustion engine. This achieves the result that a change in the actual moment and thus any bucking, etc., can be detected with the help of the rpm sensor which is already present anyway. This avoids the need for additional sensors or other additional components.
In an advantageous embodiment of the present invention, irregular running values are determined for the individual cylinders. Changes in the actual moment of the internal combustion engine can be deduced from these irregular running values. It is thus possible with the help of irregular running values to detect fluctuations in rpm or bucking of an internal combustion engine. Irregular running values can be determined in various ways. It is thus possible to provide an irregular running sensor to measure the irregular running values. Likewise, irregular running values can be derived from the rpm of the internal combustion engine, for example. It is important that irregular running values represent a measure of differences in torque between successive cylinders.
In an advantageous embodiment of the present invention, first only one of the cylinders is shifted, and thereafter at least one of the irregular running values of the shifted cylinder is compared with at least one of the irregular running values of at least one of the other cylinders. It is thus possible to determine whether there is a difference in torque between the shifted cylinder and cylinders that have not yet been shifted. In this way it is possible to determine whether there can be a difference in torque between the two operating modes between which the cylinders are to be shifted and thus whether bucking may occur.
It is especially advantageous if the other cylinders are to be shifted or not shifted as a function of the comparison. If the irregular running values of the shifted cylinder deviate significantly from the irregular running values of the cylinder not shifted, shifting can be suppressed to reliably prevent bucking of the internal combustion engine in this way. However, if there is no significant deviation, the other cylinders can also be shifted to the other operating mode. In this case, no bucking of the internal combustion engine is to be expected on the basis of the minor difference in irregular running values.
In an advantageous embodiment of the present invention, performance quantities of the internal combustion engine are influenced as a function of this comparison. Thus, when a deviation in irregular running values of a shifted cylinder from the irregular running values of the other cylinders is found, it is possible for the performance quantities of the internal combustion engine to be influenced in such a way as to minimize or eliminate this deviation. Shifting that has been started can be terminated to prevent bucking of the internal combustion engine. However, it is also possible to complete shifting, so that performance quantities are not influenced until subsequent shifting.
In an advantageous embodiment the influence on one of the performance quantities is implemented adaptively. There is thus a permanent correction of the shifting operation. It is thus possible, for example, to compensate for changes in the internal combustion engine, in particular wear phenomena, etc., over its lifetime. It is also possible to compensate for deviations between different internal combustion engines of the same type during startup.
In another advantageous embodiment of the present invention, the influence on one of the performance quantities is not implemented until the next shifting operation. This achieves the result that calculations according to the present invention can be performed between two shifting operations, so that sufficient time is available for them.
It is especially advantageous if the injected fuel mass is influenced in the sense of an increase in particular in the first operating mode. It is also advantageous if in the second operating mode, the firing angle and/or the firing point is influenced in the sense of a retard adjustment in particular. Due to these measures it is possible to influence the actual moment of the internal combustion engine when irregular running is detected during the shifting operation and thus reduce the irregular running. In particular, the two operating modes approach one another at the shifting point as a result of these measures.
Implementation of the method according to the present invention in the form of a control element provided for a control unit of an internal combustion engine in a motor vehicle in particular may be especially important. A program stored on the control element can be run on a processor, in particular a microprocessor, and is suitable for carrying out the method according to the present invention. In this case the invention is thus implemented by a program stored on the control element, so this control element with the program represents the present invention in the same way as the method which the program is suitable for executing. In particular, an (electronic) storage medium such as a read-only memory can be used as the control element.